EDIT:
I realized that I have the same problem with youtube videos using adobe flash player (pepper flash the latest)

EDIT 2:
I linked time of problem appeared and using data from that information I downgrade ati-drivers to 12.6 and xorg-server to 1.12.4 and currently problem existing only with xv output in mplayer and vlc so I switched to opengl.

I can say that problem is partially solved. People who wants to discuss are gladly welcome.

EDIT 3:
Also trying on nvidia 8600 GT on another device running Gentoo and I experience movie tearing only in pepper flash. So I downgrade xorg-server to 1.12.4 but my observations are not indicate on xorg-server issue.
But every single output in mplayer (vdpau, opengl, xv) and vlc (opengl, xv I couldn't properly turn on graphics card acceleration) works great without any tearing effects.